Heat detection



Feb. 25, 1964 J. E. LINDBERG, JR

HEAT DETECTION 2 Sheets-Sheet 1 Filed May 25, 1959 e Fla. 3

Fla. 5

INVENTOR. l ./o/-nv t. L//voBE/QG, JR. BY @M44 ATTORNEY Feb. 25, 1964 J. E. LINDBERG, JR-

HEAT DETECTION 2 Sheets-Sheet 2 Filed May 25, 1959 5035 i FLUIDAT T2 REFERENCE FLUID AT T,

INVENToR. ./oH/v mbsf/es, JR. BY i Y'OKNY indicator or control United States Patent Oliice 3,122,728' Patented Feb. 25, 1964 s,i2z,72a HEAT DETECTIN .lohn E. Lindberg, Jr., Lafayette, Calif. (M24 Adrienne Drive, Alamo, Calif.) Filed May 25, 1959, Ser. No. 815,406 4 Cllaims. (Ci. 340--229) This invention relates to improvements in method and apparatus for heat detection.

The invention is characterized by its provision of a novel non-electric heat-detecting element or sensor able to detect at any of a wide range of critical temperatures. Only the detecting sensor need be located in the heatdetection Zone, and it is connected to an electrical warning or corrective system outside the zone by a novel instrument that l term a responder. The responder may most conveniently be located outside the zone in which detection is desired, though usually close to it. The actual alarm or heat-condition indicator can be connected to the responder by a wire of practically any desired length. For example, the non-electric heat-detecting sensor may be inside a house, the responder just outside the house, and the indicator at the re station. Or, the non-electric heatdetecting sensor may be zone l of an aircraft engine, ahead of a tire wall; then the responder may be behind the fire wall, and the indicator on the aircraft instrument panel.

Furthermore, the novel heat-detecting sensor may be iilamentary, a long, very-narroW-diameter, hollow tube, which may extend along a line, around a circule, or along any desired path and for practically any desired length.

An outstanding feature of the invention is that the warning circuit can be operated at an impedance of less than one ohm. This feature greatly increases the reliability of the system, for this impedance is so low that complete immersion of the circuit in water does not seriously aifect its operation.

A further object is to provide a temperature detector capable of indefinitely recycling to give Warning each time a critical elevated temperature is reached and to withdraw the warning each time the temperature drops.

Another object is to provide a completely hermetically sealed heat-detection transducer, completely free from environmental errors caused by such things as pressure and altitude changes, moisture condensation, and so on.

Another object of this invention is to provide a system which will both: (l) detect and warn when the average temperature of the continuous detecting element or sensor exceeds a pre-set warning level, and (2) give overheat warning when any small section exceeds a chosen higher temperature, and (3) give a lire warning when any section of the transducer exceeds the re temperature, e.g., 1500 F. or above.

An additional object is to provide a device capable of indicating average temperatures in two Well-deiined temperature ranges. Further, sharp changes in the pressuretemperature response characteristics, which occur at the transition point between these two ranges, may be utilized to indicate certain temperature conditions.

A further object is to provide apparatus for detecting two different average temperatures with a single instrunient.

Another object is to provide a diiferential temperature indicator.

Other objects and advantages of the invention will appear from the following description of several preferred embodiments thereof.

in the drawings:

FlG. l is an enlarged view in elevation and in section of a simplified form of temperature detection system, showing the responder and a heat-detection sensor, broken in the middle to conserve space. The electrical circuit is shown diagrammatically.

FIG. 2 is a greatly enlarged View in elevation and in section of a portion of one preferred form of a heat-detection sensor of this invention.

FIG. 3 is a View similar to FIG. 2, of a modified form of sensor, also embodying the principles of the invention.

FIG. 4 is a view similar to FIG. 2 of another modified form of sensor.

FIG. 5 is a view similar to FIG. 2, of still another modified form of sensor.

FIG. 6 is a view similar to FIG. 1, showing a somewhat different responder structure in conjunction with a different type of connection to a different electrical circuit.

FIG. 7 is a view, partly in elevation and in section and partly diagrammatic, of a differential temperature indicator embodying the prinicples of the invention.

FIG. 8 is a view similar to FIG. 7, of a further modification of that device.

GENERAL STATEMENT OF THE INVENTION As shown in FIG. 1, the temperature detection system of this invention comprises (l) a non-electric detection means, preferably in the form of a generally iilamentary senor A, (2) a responder B, and (3) an electrical circuit C. The sensor A is made of indeterminate length and does not include any element of the electrical circuit C or any other electrical circuit. Its function is to actuate the responder B, and the function of the responder B is to actuate the electrical circuit C in response to predetermined conditions of temperature obtaining in the environment Within which the sensor A is located. Thus, the sensor A and the responder B, considered together, comprise a transducer.

The sensor A may be further delined in general terms (see FIGS. 1 5) as a generally lamentary enclosure D of extended length connected to the responder B and containing means E responsive to heat in the environment of the sensor A, for raising the pressure in the responder B.

The responder B may be thought of as typically a pressure-actuated electrical switch that opens or closes the electrical circuit C in response to pressure changes induced by the sensor A as it responds to heat.

The electrical circuit C may be a warning circuit or a remedial circiut. Several responders B may be used in one circuit, if desired, to control it in some manner that depends on the temperature conditions of the environments to which the sensors A are exposed.

DETAlLED DESCRIPTION OF SOME PREFERRED FORMS OF THE SYSTEM AND ITS COMPONENTS (l) The Sensor A The temperature detector of this invention includes a novel detecting means or sensor A. The sensor A has an enclosure D, preferably comprising a narrow-diameter metal tube of constant cross-sectional area and of any desired length. Within this enclosure D is means E responsive to the temperature of the enclosure D for varying the pressure inside the enclosure D. This means E may also be referred to as a transducing agent or as a gasemitting agent. The enclosure D is gas-tight and its only opening is connected to the responder B, which itself denes a closed chamber connected to the enclosure D. An alteration of the internal pressure Within the enclosure D therefore alfects the responder B.

(a) The transduczlng agent E.-This invention depends, in most aspects, upon the ability of certain classes of substances herein called transducing agents E, to release or emit large volumes of gases or vapors when elevated to a temperature sought to be detected. When these materials Yare enclosed in a constant-volume container D and subjected to temperature changes, the resultant alteration of pressure within this container D is employed to actuate the responder B to close or open a Warning system C.

Several basic types of materials are suitable transducing agents E: (1) materials that retain gas at low temperatures and emitgas progressively over a Wide range of elevated temperatures; and (2 materials that retain relatively small quantities of gas at low temperatures and absorb large quantitiesof gas as the temperature iselevated over a Wide range.

Although these two types of materials and their characteristic phenomena have been observed for many years, about the only practical applications of them heretofore have been in the vacuum tube industry to take up yresidual gases inthe tube after sealing.

Class (1) above includes heatfdissociable materials such as the alkalineand alkaline earth hydrides, the hydrides of certain metals, listed below, and some borohydrides. These materials, when subjected to an increase in temperature, *emit Agas and therefore may b e employed as a means for altering the internal Apressure of a container D in which they are enclosed. With the alkali and alkaline earth metals, ie., groups I-a and lvl-a of the periodic table, Vhydrogen forms stoichiometric compounds such as sodium hydride and calcium hydride. These are ionic in behaviour, with hydrogen as the negative ion. The reactions are reversible and exothermic and are useful in this invention. Specically, hydrogen reacts with lithium, sodium, potassium, rubidium, cesium, calcium, radium, strontium, francium, and barium, in stoichiometric proportions to `form hydrides.

Hydrogen reacts with aluminum to form aluminum hydride and complex alumino hydrides such as lithium alumino hydride, magnesium alumino hydride, and sodium alumino hydride.

With the elements of groups III-a (including the rare earth and actinide elements), lV-a, V-a, hydrogen forms pseudo-hydrides. The solubility of hydrogen in elements of these groups varies as the square root of the pressure, and it decreases with increase in temperature. Above about 300 C., palladium also behaves in this Way. Elements of these groups are designated as group B, the class consisting of scandium, titanium, vanadium, ytterbium, zirconium, niobium, hafniurn, tantalum, the rare earth metals (atomic numbers 57 through 71), and the actinide meals (atomic numbers 819 through 103); palladium is a member of this group at temperatures greater than about 300 C. This solution is commonly termed a hydride, though it is not a stoichiometric compound. Examples of the sorptive capacities as a function of temperature of some materials chosen Yfrom the hydrides of group B are given in Table I.

TABLE L SORPTION OF HYDRQGEN BY TYPICAL META-LS OB GROUP B [In cm (S.T.P.) per gm., at 1 atm.]

TABLE IL ADSORPTION OF GASES BY CHARCOAL [Volume of gas per gram adsorbent, adsorbed at 151 C. and 760 mm. pressure] Gas: Vol. adsorbed in cm..3

`Cool2 44o NH3 1 S 1 O2 m n 8 H2 5 Several zeolites exhibit marked capacities for sorption and desorption. Illustrations or" some typical solubilities of hydrogen and carbon dioxide in dehydrated chabasite, a form of zeolite, Vare shown in Table lll.

,TABLE rrr-sonr'rroN 0F HYDROGEN AND CARBON Droxron [By dehydrated ehabasite at 0 C. and 760 mn'n] T, C C D V0 T, O D V0 6l. 4 0. l 120 33. 2 33 91. 3 1. O 390."- 9i). 7 12?: 97. 5 2. 7 635 96. 3 115 Where:

D=percentage of dehydration, and Vo=amount occluded iu cm/gm. at standard temperture and pressure.

All these are merely example of class (1) materials as deined above, and do not by any means exhaust the list. `lor the purposes of this invention, however, they do exemplify the materials that retain gas at low temperatures Aand emit gas progressively Vas the temperature is raised.

Class (2) materials, in contrast to those of class (l), absorb gas when subjected to a temperature elevation. They .also may be employed to alter the internal pressure of a container in which they are enclosed. For example, hydrogen interacts with what are known as the group A metals, consisting of copper, silver, molybdenum, tungsten, iron, cobalt, nickel, aluminum, platinuaninanganese, technetium, rhenium, osmium, iridium, ruthenium, and rhodium; chromium is a member of this group at temperatures greater than `about 399 C. lThe action appears to be a type `of solubility, and the solubili-ty in creases with increasing temperature. Certain borohydrides also behave in this manner. Examples of the sorptive capacities of typical class A materials are illustrated in Table lIV.

TABLE IV.SORPTION OF HYDROGEN BY TYPICAL vllIlLTALS OF GROUP A [In 0111.3 (S.T.P.) per 10() gms., at 1 atn1.]

Temperature, C. Nickel Copper Chromium Temperature, C. i Titanium I Vanadium Zrconium Oxygen also reacts similar-ly with some metals, but in many cases it is diilicult to distinguish between solution of oxygen and solution of oxides. However, the formation of true solutions` has been determined in silver, copper, cobalt, .and a few other meta-ls. `Examples of the solubility of oxygen in silver and copper are listed in Tables V md TABLE V.-SOLUBILITY OF OXYGEN IN SILVER AT 1 ATM. PRESSURE T 1C. Cm/li g. 40() 0.83i 60() 1.26

TABLE VI.-SOLUBILITY F OXYGEN IN COPPER AT 1 ATM. PRESSURE T., C.: Cm.3/100 g. 600 .t. 5.0

Many other examples may be cited of gases dissolving in metals. The omission of others is not intended to exclude them from this invention.

With materials of this invention, the process of sorption yand desorption is reversible. Thus a sample of such material may be subjected to the sorption and desonption process for .an indefinite number of repetitive cycles.

The materials of this invention, as explained previously, when Ilocated within a closed chamber, provide an effective means of altering the internal pressure of the chamber. This internal pressure, as explained in my copending application Serial Number 759,717, filed September 8, 1958, is a function of the temperature applied to the material. ln general, there exists a one-to-one correspondence between this pressure and the temperature. Thus, the enclosed material functions as an element which effectively converts temperature variations into pressure. variations and that is why the general class of materims is referred to herein as transducing agents.

(b) Typical sensor structures-FIGS. 2-5 illustrate a few of the many ways in which the sensor A may be constructed. Transducing agents E may be used in a lilamentar, peliet, or granular form, always being placed inside the sensor tube D which may be a non-porous tube of constant cross-sectional area. ln applications where the tubes D are to be bent or curved around corners, metal is the preferred material. Suitable metals are pure iron, which is impermeable to many gases, stainless steel, and molybdenum, for example. ln applications where bending is not required and minimum diffusion is desired, the tube D is pre^erably made from non-porous quartz, ceramic, or special glass. In any event, the inner surface of the tube D should not react with the materials it contacts, including the gas involved. Where the tube D is reactive with the transducing agent E, a special problem is created, which I solve as described below. A typical sensor tube D is preferably about 0.040 t0 0.060" outside diameter with a wall thickness of preferably about 0.605 to 0.015". Such tubes D are preferably about two to twenty feet long, although they may be longer or shorter.

2 shows a preferred form of transducing agent E enclosed in the sensor tube D. Here the transducing agent E is a lilament 7d, such as zirconium wire for group B operation or copper wire for group A operation, and may be about 0.025 to 0.050 in diameter, for example. A ribbon 71 of suitable material, such as molybdenum, preferably about 0.02.0 wide and 0.002 thick, is wrapped tightly around the iilamentary transducing agent 76 and fits snugly within the tube D. The ribbon 7i physically spaces the iiiament 70 from the walls 72 of the tube D and prevents the transducing agent 70 from fusing or welding to the tube walls 72, even in the event that the sensor A is exposed to extreme heat.

As a simpliied example of installation of the sensor A of FIG. 2 to the responder B, one end 73 (FIG. l) of the tube D may be connected by a gas-tight seal to the responder B, while the other end 74 of the tube D is still open. This free end 7d may be connected to a vacuum pump and the tube D pumped free of gas. Then the tube D is heated, and then pure hydrogen is forced in through the free end 74, the zirconium filament 70 absorbing the hydrogen while it cools. When group A material is used, hydrogen may be pumped into the tube D while the wire 7d is heated, thus ingassing it at an elevated temperature. ln either event, the originally pure metal 70 is converted into an ingassed hydride. The free end 74 is then sealed oif, and the device is ready for operation.

In the sensor A of FIG. 3, the transducing agent E may consist of powdered hydride molded or pressed into the form of a tube '75. Hydride may be held in this form by using a suitable binder, which may be hydrolized ethyl silicate. The hole 76 which extends axially along the length of the tube 75 serves as the free volume space through which evolved gas may ow. The tube 75 is fitted snugly into the tube D, the tube-end '73 connected to the responder B, the tube D processed as described above or as desired, and the end 7 4 sealed.

The transducing agent E may be used in the form of a series of discrete pellets 77 as shown in FIG. 4. The pellets 77 may be formed by molding or by dispersing powdered hydride, for example, in a binder such as hydrolyzed ethyl silicate and compressing the mixture into pellet form. The pellets 77 are made slightly smaller than the inside diameter of the tube wall 72 to allow passage of gas evolved from the pellets 77.

ln FIG. 5 the transducing agent E comprises a series of small granules 78 within the tube D. These granules may be number 40 or 70 grit size of titanium hydride or zirconium hydride, for example.

Although only a few specific forms for the agent E have been illustrated or described, many others are possible, and it is intended that their omission not be in any sense limiting or restrictive to the possible application and construction of this invention.

Thus, the combination of the tube D and the transducer agent E functions as the heat-sensitive element or sensor A in this fire detector.

ln FIG. 1, the sensor A may contain a hydride of group B, such as zirconium hydride. At ordinary temperatures this compound will retain its hydrogen until it is heated to or above a certain threshold temperature. At such a threshold temperature, degassing of the compound will begin to occur, during which some of the hydrogen will be emitted and liberated as a gas, thereby increasing the pressure inside the tube D. As stated earlier, one end 74 of the sensor A is sealed while a pressuresensitive switch or responder B is sealed to the tube D at the other end. Let us now consider the responder B.

(2) A simple form of responder B FIG. l)

Any pressure switch that is properly sensitive and has the needed connections may be used as a responder B. However, I have invented a new pressure switch that is especially suitable for use herein.

FIG. l shows a simple form of responder B, suitable for simple installations. This responder B comprises a unit 80 and has two circular plates 81 and 82, preferably of non-porous metal, between which is bonded (as by brazing) a thin metal liexible disc or diaphragm 83. The plates 81 and 82 are hermetically sealed together and are .in electrical contact for their full peripheries and over a substantial margin, but in the center the diaphragm 83 has a spherical depression 84 called a blister, which is free to move relative to the plates 81 and 82 and constitutes the active or movable part of the diaphragm S3. Use of a diaphragm with a blister 84 makes possible the use of an upper plate S2 with a planar lower surface 85 and gives a more predictable response, but other diaphragm structures may be used where feasible. The lower plate 81 is formed with a recess 86 in its upper surface, and the diaphragm 83 divides the resultant cavity between the plates into two regions or chambers 87 and 88. Since the lower region S7 communicates with the sensor A, it may be called the sensor chamber. The other region 88 is located on the opposite side of the diaphragm S3 from the sensor A; so it may be called the anti-sensor chamber. Of course, either plate 8l or 82 may actually be made by brazing together several thin plates of the desired conguration, and the recess 86 may be provided by using a stack of preformed thin washers over a disc. A preferred material for all the metal elements in the responder 80 is molybdenum.

The end 73 of the sensor tube D is joined to and sealed to the lower plate 81, iitting within a hole 90. The region 87 is closed and sealed except Ifor its communication with the lumen of the sensor tube D; so the inside of the sensor A and the sensor chamber 87 enjoy a cornmon atmosphere to the exclusion of any other.

A tube 91 of Anon-porous ceramic material or other non-porous electrically-insulating material extends through an opening 92 in the upper plate 82 and is hermetically sealed in place there with its lower end 93 flush with the bottom surface 85 of the plate 82. The hole 92 and tube 91 are preferably centered with respect to the blister 84, on the anti-sensor side thereof. A metal electrode 94 is located inside and joined securely to the tube '91 at the end 93 nearest the blister 84, with a portion 95 of the electrode 94 extending below the lower surface 85 of the plate 82. The amount by which the portion 95 extends below the surface `85 is carefully controlled so as to be uniform in each responder of any particular design. This geometry means that the blister 84 can make electrical contact with the electrode portion 95 when the blister 84 is forced up by pressure in the sensor chamber 37. As shown, the electrode 94 may be annular to give good uniform contact with the blister 84 lat that time and also to afford communication between Vthe blister $4', it will deilect and make contact with the electrode portion 95, and if the deecting force is removed the restoring force of the blister 84 will return it to its relaxed position and thus break contact with the electrode portion 9S. The force necessary to do this may be chosen by proper design of the blister to accommodate a wide range-of values.

(3) A Simple Crcuit'C and its Operation (FIG. 1)

As explained before, the responderB may be connected to an alarm circuit which, as shown in FIG. 1, is a simple visual indicator consisting of a lamp 100 in series with the conducting wire V97 and a source 101 of electrical current, which may be a battery as 'shown or V may be a source of alternating current. A return path for the electrical circuit C may be provided by grounding either one of the plates 81 or 82 and is shown as a ground wire 102 in FIG. 1.

In operation, when `the sensor A is exposed to heat at a level high enough to cause the transducing agent E to rise above its threshold temperature, gas is emitted. This gas cannot escape from the sensor tube D except into the sensor chamber 87, where it exerts pressure upon the blister 84. This pressure tends to move the blister 84 away from the plate 81 and toward the plate 82. The pressure in the'sensor chamber y87 is a function of the temperature of the sensor A, and in general there will be a one-to-one correspondence between the temperature of `the sensor Ay and the pressure with the sensor chamber 87. This pressure, if great enough, will cause the blister 34 to make contact with the electrode 94, but no contact will be made unless Vthe temperature of the sensor A is at or above a definite level.

When the sensor A is exposed to heat at a level high enough to cause the blister 84 to make contact with the electrode 94, current ilows from the battery 101 through the lamp 10Q, the conductor 97, -the electrode 94, and the blister 84 to the plates S1 and 82 and returns to the battery v101 through ground line l102. This current ow causes the lamp 100 to light and provides a visual indication that the temperature of the sensor A is at or above a certain level. In this sense, the device shown in FIG.

1 functions as a threshold temperature indicator. When heat is removed from the sensor A, the transducing agent E cools and reabsorbs its previously emitted gas, resulting in reduction of the pressure exerted upon the blister 84. The blister 84 moves away from the electrode 94, breakin-g the electrical circuit, and the lamp goes out.

In practice, the sensor A is placed in the area whose temperature is to be monitored, while the responder B may be located upon or behind a shielded Wall 103 or at some easily accessible area. Thus only the sensor A itself need be exposed to possible heat sources, and it contains no element of vthe electrical circuit. In this manner, protection for the responder B and its associated alarm circuit C may be provided.

(4) Some Ways of Setting the Theshold Temperature (FIG. l

The force necessary to deilect the blister S4 against the electrode 94 can be chosen to accommodate a wide range of values by a suitable choice ot mechanical parameters. Once this force is determined, the dimensions of the sensor tube D and the amount of transducing agent E may be chosen by design to provide the force necessary to obtain contact between the blister 84 and electrodes 94 at a certain temperature.

In addition to mechanical design considerations, the necessary deecting force may also be altered by precharging the anti-sensor chamber yS8 with a gas under pressure or by partially evacuating it. To accomplish this, gas is forced into (or withdrawn from) the tube 91 after its attachment to the plate 82 and before it is closed by its cap 98. The required deflecting pressure against the blister 84 becomes greater as more gas is present in the chamber 88.

Alternatively, the deecting pressure may be effectively lowered by precharging the inside of the sensor tube D and the sensor chamber S7 with gas. In this case, if the ambient pressure in the sensor chamber S7 is greater "than normal, less than normal gaseous elaboration from the transducing agent E is required to deflect the blister 84 against the electrode 94.

Most gases may be employed for this purpose; however, 'ideally the gas should not react chemically with its surrounding materials. Particularly suitable are the inert gases, such as helium, argon, neon, and xenon, especially since they do not readily diuse through most materials. As a consequence, a precharged pressure of argon, for example, may be maintained for an indefinite length of time 'to retain a desired biasing of the diaphragm 3, as

described.

(5). A -Modijed Form of Simple Responder B and its Modied Circuit C. (FIG. '6)

The responder B may Ialso be so used that the variations in lpressure occurring on the anti-sensor side of the diaphragm '83 will act indirectly on an auxiliary pressure switch. In this case, the blister M84 does not close against `an electrode. In the unit shown in FIG. 6 there is Vno electrode, but a ceramic tube 1111 is inserted in the responder 110E as before with its interior 112 in direct communication with the anti-sensor `chamber 38 and, also, via an arm 113 of the tube 111, with a conventional type of pressure switch 114. This switch 114 may be, for example, one whose contacts 115 and 116 close when pressure is applied to a piston 117.

Thus, when the sensor A is heated, the diaphragm blister S4 is deflected toward the ceramic tube 111 and causes an increase of pressure in the anti-sensor chamber 8 and tube interior 112, which in turn is communicated to the `pressure switch 114. At the selected pressure, the con- 'tacts 115 and 116 of the pressure switch 114 close, and

current flo-Ws Yfrom a battery 118 through an auxiliary control 119. This control 1119 may be a lamp like the lamp 100, or it may be a device to perform any other suitable function, such as, .for example, to operate a fire extinguisher. (Of course, the lamp 100l in FIG. l may also be replaced by such a control 119.) When the temperature of the sensor A falls below a certain value, the blister 84 re-deflects toward the sensor A to its normal position and decreases the pressure within the ceramic ltube 111, thereby deactivating and opening the pressure switch i114. The auxiliary control 119` then ceases to function.

Alternatively, the pressure switch 114 may be such that its contacts 115' and 116 are normally closed. Then when the pressure in the interior 112 of the ceramic tube 111 is increased beyond a certain value, the applied pressure to the switch 114 opens its contacts 115 and 116. This action may be used to perform various suitable functions. For example, it may function as a thermostat. lt also enables the use of type v(2) transducing agent, suc-h as copper hydride, which ingasses as the temperature rises and outgasses when the temperature drops.

Pre-conditioning of the test element.-When most metal hydrides are purchased, it will generally be found that they are over-charged with hydrogen. Also, metallic hydrides are partly electrically conductive, and their conductivity changes with temperature. At high voltages or at high temperatures, the hydride may short-circuit the filament. Therefore, more consistent and more accurate results are obtained by pre-conditioning the hydride.

One way of solving the electrical resistance problem just stated is to electrically insulate the hydride particles at all times, without inhibiting the passage `of gas to or from the hydride. A unique way of accomplishing this is to intimately mix hydride particles With an insulating material such as powdered alumina or quartz. The particles of insulating material may be the same size as the hydride particles, or smaller, down to microscopic size. In the construction of test units, it was determined that ball-milling a rnix of either microscopic or particulate alumina and titanium hydride in equal parts by weight for several days produced a very satisfactory result. Test assemblies employing filaments of 0.002 diameter tungsten vvire embedded in this mix have withstood cyclic and continuous operation for periods of several hours without mechanical or electrical failure and without noticeable change in operating characteristics.

Additional advantages derived from the use of the hydride-insulator mix are that much less filament current is required to cause a given amount of gaseous elaboration than is necessary when unprepared hydride is used, indicating an increase in the energy transfer efficiency.

(6). The Behavior of Various Transducz'ng Agents E The operation of the illustrated systems has hereto-fore been described mainly with reference -to group B hydrides as the transducing agents. However, all these systems will also function with any of the other transducing agents previously described. Which one is to be preferred depends on the purpose to lbe served.

Class (2) materials elaborate gas when the temperature is lowered Suppose, for example, that nickel hydride were used as the transducing agent E. The apparatus of FIG. l may be -made so that the blister 84 is in its relaxed position when the sensor A is exposed to a temperature of `600" C. Then, .if the temperature at the sensor A is lowered to, say 200 C., hydrogen will be emitted from the nickel hydride and deflect the diaphragm 84 against the electrode 94, energizing the `alarm circuit C. In this case, the illumination of the lamp 100 indicates 4that the temperature in the area to which the sensor A is exposed is at or below 200 C. The reaction is reversible; so when the sensor A is again heated to 600 C., the nickel hydride reabsorbs its previously emitted hydrogen and the diaphragm 184 returns to its relaxed position, deenergizing the yalarm circuit C. In this example the device was employed to indicate a temperature drop,

10 but it will be apparent that it can be used to indicate temperature elevation as well by having the warning actuated by a circuit break instead of a circuit make. This technique is -well known and need not be described in detail.

Average temperature indication versus spot temperatures-The heat-detecting apparatus of this invention as so far described indicates the average temperature to which the sensor A is exposed. The sensor A is not usually exposed to the same temperature uniformly along the tube D; the high temperatures usually affect only certain localized regions of the tube D, while the remaining regions are at a lower temperature.

The material used in this invention outgas and ingas reversibly. As a result, gas emitted by localized heating of the sensor A may be reabsorbed in the cooler portions of the sensor. For example, if a tube D containing a class (1) agent E is locally heated, the resulting increase of pressure disturbs the equilibrium conditions around the material in the cooler portions of the tube D yand some ingassing takes place there. This counteractivity does not, however, mean that the average pressure in the tube is the same las it was before any heating was applied. Actually, if the transducing agent E is fully ingassed, the average pressure is elevated by this process, and the responder B thus responds to the average pressure in the tub-e. This, in turn, means that the alarm circuit C still indicates the average temperature to which the sensor A is exposed. For example, if half of the tube is exposed to a temperature of 850 C. and the remaining half is exposed to 750 C., the response of the alarm circuit C will indicate that the average temperature is approximately 800 C.

The heat-detecting apparatus of this invention may be made to operate effectively over two distinct ranges of average temperature indication. This type of operation enables a unique determination of any preselected yternperature occurring above a certain value.

One range of average-temperature response is that in which the transducer agent E takes in or emits gas freely. This response has already been Idescribed and applies only above the threshold temperatures of the material.

The other range of average temperature operation is below the threshold temperature of the particular transducing agent E involved. Class B hydrides, for example, 4do not emit gas until a certain temperature-pressure condition is reached.

The lthreshold point is there-fore the meeting point of the two ranges. Below the threshold point, the gas in the sensor A surrounding the transducing argent E behaves very nearly as -an ideal fgas obeying the well-known laws of gases. The volume remaining constant, an incre-aise in temperature results in an increase in pressure. At various points along the sensor A the temperature may vary, 'and the pressure in the tube D results from the total effect of the incremental expansions at each incremental portion of the tube along its length. The sensor A has a constant cross section and enoloses almost all the volume on the sensor side of the blister 84 (FIG. l), which is verry nearly constant, since the change in volume due to` diaphragm movement is negligible. Hence the pressure in the tube D averages out `the variations in temperature, and the responder B is actuated by the average ternperature to which the sensor A is exposed. Below the threshold point the relation between the `average temperatnre applied to the sensor A and `the resulting internal pressure is very nearly linear, having a rather gentle slope.

When lche temperature of the sensor A reaches the threshold point, the transducmg agent E emits gas. Since, at the threshold point, the transducing agent E is fully ingass'ed, local heating at or above the threshold point elaborates gas lwhich is not reabsorbed by the remaining cooler portion. As a result, there is a sharp increase in the rate of change of pressure, with respect to temperature, in the tube D, and a discontinuity in the slope of the curve occurs. The new slope represents `a linear rel-ation between pressure and temperature and, in fact, the relationship is very nearly linear over a wide range of conditions above the threshold point, for as the average temperature is elevated above the threshold point, the itransducing agent E is no longer fully ingassed, and the device again functions las an average temperatur-e indicator, but with a steeper slope.V

The threshold point is uniquely determined by the type of transduoing agent E employed, together with the initial pressure of gas in equilibrium with the agent E and the mechanical design of the system. A wide range ori threshold points may thus be availed of by proper design.

As explained earlier, the gas surrounding the transducing agent E below the threshold point may either be the gas vwhich is taken up or released by the argent or may be `an inert gals. The inert gases are preferable, since they are less likely to be lost by diffusion through the tube D, than is hydrogen. Also, inert gases do not affect the Adegree of ingassirsg of the transducing agent E.

Shruper detection of the threshold point is obtained by eliminating lthe inert gas and operating the agent E under vacuum conditions, thereby making it possible to detect a threshold temperature applied to only a short length of the tube D. As before, choice of the agent E, its degree of ingassing, and the sensitivity olf the responder B may be varied to change the threshold point. Alloys of agents E may be used.

(7). Difierezztial T emperatnre Indication (FIGS. 7 and 8) (o) A two-Sensor indicator (FIG. 7).-FTG. 7 shows a :differential temperature indicator 56) employing a moditied form of responder 501, two sensors 592 and 503, an indicator or control device &4, and a current source 5%. The responder Sill comprises ltwo pilates Silo and 5in, a diaphragm 5nd with two blisters 569 and 510, land two tubes 51T and Sli ou. insulating material. Con- 'facts Sl and 5&4 are connected by respective wire `leads 515 and 5116 to the indicator or control 594. The convex sides of the blisters 5l9 and 510 are on opposite sides of the 'diaphragm 568 and serve to separate the interior of the responder 5h11 into two gas-tight chambers '517 and 5rd. The chamber 517 includes the interior of the sensor 5%, a small duct `51S?, and the interior of the tube 511; the chamber 5118 includes the interior of the sensor 502, a small duct 524i, andthe interior of the tube 5&2. Each sensor 5%2, 503 contains a transduoing agent 52d, '522, such as zirconium hydride wrapped with vmolybdenum ribbon. The electric circuit is completed by la ground connection 523 ot the responder 561.

The sensors 502 and `503 may be exposed to environments whose temperatures it is desired to compare. Emission of gas by the transducing argent 522 in the sensor 5% increases the pressure in the chamber 517 and tends to cause the blister 599 to move toward the contact 51st and the blister 519 to move away from the contact '533. Emission ot gas by the transduoing agent 521 in the sensor 5012 tends to `have the opposite effect by increasing the pressure inthe chamber 518.

The responder 561, and particularly the diaphragm 56S, may be designed so that both vblisters 509 and 510 touch their contacts 514 and 513 only at a certain welldeined pressure diierence between the chambers 517 and 518. If the pressure inthe chamber 518 is too high, the blister 5b@ will move away from its contact 514; if too low, the lister 5l@ will move away from its contact 5H. The pressure dierence at which both blisters 509 and 5i@ touch their contacts 5l4'and 513 can be chosen from a wide range by design of the components. The conditionin which both blisters 5539 and 51u touch their contacts 521.4, 5131may be called the null condition.

Since the pressures in the chambers 517 and 518 depend upon 'the temperatures of the sensors 5%?, and 502,

the difference between the pressures in the chambers 5l? and 5313 depends upon the difference between the tempe'ratures of the sensors 5% and 502. Over the linear ranges of the transducers pressure-temperature curve,

P1 is the pressure in the chamber SES,

P2 is the pressure in the chamber 517,

T1 is the temperature of the sensor 502,

T2 is the Vtemperature of the sensor 563, and

al, a2, and b are constants which depend upon the initial pressures in the chambers 517 and ST8 and on the transducing agents 52T and 522.

subtracting the rst of these equations from the second gives the result or, deining (P2-P1)==AP, (T2-T1)=AT,v and (a2-a1)=A, AP=AlbAT- Therefore, if it is desired that the null condition o the responder Stil occur at a particular temperature diierence ATO between the 'sensors 5&2 and 5%3, the above equation gives the value of APO for which the responder should be designed to be in the null condition. To achieve APO, the blisters 599 and 5l@ can be made more sensitive or less sensitive by changing their diameter, thickness, and concavity, and the initiai pressures in the chambers 517 and 518 may be adjusted, as discussed previously.

The indicator 504 is designed for null indication when the responder 591 is in the null condition. Otherwise, the indicator 5% gives one of two .possible signals, which one depending upon which blister, 599 or 510, is not touching its contact, ST4 or 513. The signal given by the indicator Silit may be merely a warning to alert an operator that something is wrong, or it may serve to actuate an automatic control which can remedy the trouble.

Suppose that it is desired to maintain a fluid stream at a temperature T2 which is AT degrees above the temperature T1 of a reference stream. The responder 501 is constructed to be in the null condition when the sensor 503 is AT degrees warmer than the sensor '562. Then, the sensor 5% is placed in the stream at temperature T2 and the sensor 5%2 is placed in the reference stream at temperature T1. No matter what the temperatures T1 and T2 are, as long as their dii'erence (TT-T1) is equal to AT, the responder 501 will remain in the null condition. It", however, the temperature T2 of the fluid stream surrounding the sensor 5&3 rises while the temperature T1 at the sensor 502 remains steady, the pressure iu the chamber 517 rises land causes the blister 510 to leave the contact 513. The indicator 504 then gives a signal to notify an yoperator or actuates an automatic control to cool the stream surrounding the sensor SES or to heat the stream surrounding the sensor 502, thus bringing the responder iii back to the lnull condition. If the tempera- -ture T2 drops relative to T1, then .the blister 569 leaves the contact 5M. In this case, the indicator 504 gives the other signal to notify the operator or actuates the control to heat the stream surrounding the sensor 503 or to cool the stream surrounding the sensor 502.

(b) vUse of heated sensors (FIG. 8).-The device of FIG. 7 ymay be modiied to provide a comparison of the rates of flow of two fiuid streams past the sensors 5ll2 and 5%. The modification comprises the addition of means for `heating Vthe sensors; for example, current may be passed through them, as shown in FIG. 8. Current from a battery 53th lows through a potentiometer 531 where it divides, part going through a wire 532, the sensor 592, and the responder Sill, and `returning to the battery 539 via the ground lead 523. The other part of the current from the battery 530 goes through a wire 533, the sensor 5%, and 'the responder 501, and returns to ythe battery 535i via the ground llead 523. The rest of the device of FTG. `8 is vthe same as'thatof FTG. 7.

The current flowing through the sensors 502 and 503 dissipates power in their resistance and heats them.V If the power dissipation is constant, the equilibrium temperature of each sensor depends upon the rate at which heat is removed from it. Since a fluid in motion removes heat from an object immersed in it faster than a still uid, the rate of heat removal being an increasing function of the uids velocity, the equilibrium temperatures of the sensors 502 and 503 depend upon the rate of flow of the liuids past them, as well as the initial temperatures or the fluids. The relative currents through the sensors 502 and 503 can be adjusted by means of the potentiometer 531 in order to compensate for differences in the temperatures of the two fluid streams. Thus the device of FIG. 8 is a ditferential-ow-rate indicator which comparcs the rates of flow of two fluid streams and maintains them at constant magnitudes relative to each other. One application of such a device is in a process where fiuid iiows into a tank from a supply and out through a drain; in order to avoid emptying or overflowing the tank, the input and outputs ows must remain equal. The device of FIG. 8 can actuate suitable controls to maintain the equality of the fiow rates of the two streams.

Many variations of the `forms of the invention shown in FIGS. 7 and 8 are possible Without departing from the spirit and scope of the invention. For example, the quantity AT may be adjusted by adjusting the pressure in the anti-sensor chamber; or a single-blister responder may be used to give indication only when T2 is higher (rior example) than T1. The omission of discussion of such variations is not intended in any way to limit the application of the principles of this invention.

(c) Indication and control of cooling rates (FIG. 8 -Internally heated equipment, such as electronic equipment and power-generating equipment, often must be cooled by a cooling iiuid, usually gas. The amount of cooling Idepends upon the initial temperature of the iiuid as well as the tlow rate, for if the incoming fluid becomes colder, less flow is required, and if it becomes warmer, more flow is required to maintain the equipment at a safe operating temperature.

The device of FIG. 8 can be used to meas-ure or control the relative cooling of two separate -iluid streams. Flor example, the sensor 502 may be removed and the chamber 520 may be filled with gas Iat a predetermined pressure and sealed. Then the potentiometer 531 may be used to adjust the temperature in the sensor 503 until the null condition is obtained at the desired cooling condition. 'Ilhe indicator 504 twill then show Whether the cooling effect is above or below standard, and it can also be used to control the cooling as required.

For optimum operation the chamber 520 may be fully evacuated and the blister 509 designed to fully balance the desired working pressure in the chamber 519, thereby eliminating temperature errors in the reference standard. If simplicity is desired, the system may be operated with a single diaphragm 509 and the Iblister 510, electrode 513, tube 511, lead 515, passage 520, and sensor 502 may all be eliminated.

For such applications the sensor 503I preferably employs materials essentially impervious to gas diffusion, such as imporous ceramic, quartz, and special glass.

As brought out many times lherein, I utilize molybdenum metal in novel ways. For example, the molydennm ribbon 71 succeeds where ribbons of stainless steel, nickel, manganese, iron, aluminum, copper, etc. failed, because they reacted with zirconium, titanium, etc. to form alloys with eutectic points below the melting points of -the individual metals. In the operating range herein, molybdenum solves the pr-obelm; it does not 4weld to the wire 70, or plug the gas passage, or form a low-meltingpoint alloy, and it gets stronger instead of weaker in the presence of zirconium and titanium. Its effect on the hydnides is to shift the alpha-beta transition point tfavor- 14 ably, i.e., to lower it. Note -that FIG. 5 and others show the wire-ribbon combination in the fully ingassed state. When outgassed, the ribbon 71 is -loose in the tube 72, for the -wire 70 expands about 15% as a result of ingassing and contracts 'when outgassing.

Tc those skilled in the arts to which this invention relates, many changes in construction and widely diiering embodiments in applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures` and the descriptions herein are purely illustrative and lare not intended to be in any sense limiting.

I claim:

y1. A differential temperature ydetection system comprising a diaphragm; a housing divided by said diaphragm into first and second chambers; a first tube connected to said first chamber and containing a transducing agent that releases large quantities of gas when heated; a second tube connected to said second chamber and also containing a transducing agent that releases large quantities of gas when heated; a switch in each Iof said rst and second chambers, each actuated by said diaphragm as a result of the difference between .the pressures in said iirst and second chambers; and an electrical circuit for said switches and actuated thereby, said circuit including an indicator actuated by said circuit.

2. The system of claim 1 wherein there are electrical means for heating each tubes transducing agent.

3. A differential temperature detection system comprising a diaphragm; a housing divided by said diaphragm into dirst and second chambers; a first tube connected to said rst chamber and containing a transducing agent that releases large quantities of gas when heated; a second tube connected to said second chamber and also containing a transducing agent that releases large quantities of gas when heated; a switch in said second chamber and actuated by said diaphragm at a pressure difference level between chambers; an electrical circuit for said switch and actuated thereby, said circuit including an indicator actuated by said circuit; and electrical means for heating each tubes transducing agent.

4. A differential temperature ydetection system comprising a diaphragm; ia housing divided by said diaphragm into iirst and second chambers; a first tube connected `to said first chamber and containing a transducing agent that releases large quantities of gas when heated; a second tube connected to said second chamber and also containing a transducing agent that releases large quantities of gas when heated; an electrical switch in said second chamber and actuated by said diaphragm at a pressure difference level between chambers, resulting from a temperature difference between said tubes; and an electrical circuit for said switch and actuated lthereby, said circuit including an indicator actuated by said circuit.

References Cited in the file of this patent UNITED STATES PATENTS 436,045 McElroy Sept. 9, 1890 1,665,381 Siddal et al. Apr. 10, 1928 1,781,289 Mayo NOV. 11, 1930 1,907,666 Raney May 9, 1933 1,907,869 Raney May 9, 1933 2,004,667 Mautsch June 11, 1935 2,082,134 Alexander June 1, 1937 2,189,147 Mathisen Feb. 6, 1940 2,246,536 Reinthaler June 24, 1941 2,274,119 Baak Feb. 24, 1942 2,283,374 Kronmiller May 19, 1942 2,484,932 Cox Oct. 18, 1949 2,493,351 .Tones Jan. 3, 1950 2,551,526 Campbell May 1, 1951 2,566,235 Mathisen Aug. 28, 1951 (Other references on following page) v16 Smeaton Oct. 8, 1957 Engelberger June 17, 1958 Wanamakr et a1. Nov. 11, 1958 Huff Apr. 28, 1959 Poitras Mar. 1, 1960 FOREIGN PATENTS Australia Sept. 29, 1947 

1. A DIFFERENTIAL TEMPERATURE DETECTION SYSTEM COMPRISING A DIAPHRAGM; A HOUSING DIVIDED BY SAID DIAPHRAGM INTO FIRST AND SECOND CHAMBERS; A FIRST TUBE CONNECTED TO SAID FIRST CHAMBER AND CONTAINING A TRANSDUCING AGENT THAT RELEASES LARGE QUANTITIES OF GAS WHEN HEATED; A SECOND TUBE CONNECTED TO SAID SECOND CHAMBER AND ALSO CONTAINING A TRANSDUCING AGENT THAT RELEASES LARGE QUANTITIES OF GAS WHEN HEATED; A SWITCH IN EACH OF SAID FIRST AND SECOND CHAMBERS, EACH ACTUATED BY SAID DIAPHRAGM AS A RESULT OF THE DIFFERENCE BETWEEN THE PRESSURES IN SAID FIRST AND SECOND CHAMBERS; AND AN ELECTRICAL CIRCUIT FOR SAID SWITCHES AND ACTUATED THEREBY, SAID CIRCUIT INCLUDING AN INDICATOR ACTUATED BY SAID CIRCUIT. 